As it is known, the brake calipers are used in a very large range of road and railway vehicles, and aircrafts as well, and provide for the generation of a braking force through the interaction between said calipers, which are generally solid to the frame of the vehicle, and one or more discs solid to the wheels thereof.
A first type of known brake calipers comprises a single small piston, sliding within a respective seat formed on a side of the brake calipers under the action of a fluid, generally a fluid under pressure.
Such small piston is generally disposed on one side and is engaged on at least one braking pad able to mate with friction a respective side surface of a braking disc.
Also known are calipers wherein more pistons are provided disposed in facing relationship to each other.
Each caliper is also connected with an actuation device, generally a manually-operated lever or a footboard, said device being engaged by a user to generate a braking force. In the modern applications, the actuation device is operatively connected with the brake caliper through a system of conduits which put the actuation device into fluid communication with the brake caliper and is able to transmit a pressure, also of high value, to the brake caliper.
In the known embodiments, each piston is slidingly received within a respective seat formed in the body of the brake caliper, and is driven into slide motion by the action of the fluid under pressure which, in turn, is controlled by actuation means such as hydraulic pumps, for example.
The piston, therefore, slides operatively inside the respective seat under the action of the pressurized fluid, in particular to shift from a first rest position to an active position in which it exerts a thrust toward the braking disc.
The above cited fluid seal is obtained by the interposition of an elastic gasket, engaged to a side portion of the seat formed in the caliper body, which prevents the outward bleeding of the pressurized fluid. Moreover, the gasket has the function to deform elastically during the operative sliding of the piston, the latter, after completion of its working stroke, tending afterwards to move back, at least partially, to the retracted position inside the cylinder owing to the elastic return of the same gasket (“rollback” action of the piston).
Unfortunately, it has been found that the presence of fluid pressure on only one side of the gasket tends to oppose the rollback action, inasmuch as it prevents the elastic return of the deformed gasket.
Other known solutions provide for interposing, between the piston and respective seat, a pair of gaskets engaged in suitable recesses formed in the seat. A first gasket, having a proper fluid-sealing function, is located at a position further inside with respect to the piston's sliding direction, toward a bottom portion of the seat, and prevents the outwardly bleeding of pressurized oil. The other gasket, on the other hand, has a protecting function against dust.
Unfortunately, such a system requires to work out one or more recesses in the seat for fitting the gaskets.